Process for making an assembly of electrically conductive patterns on an insulating surface of complex form

ABSTRACT

The present invention relates to a process for making an assembly of electrically conductive patterns (9, 16) on an electrically insulating surface (20) of complex shape. 
     According to the invention: 
     said assembly of patterns (16) is formed on a face of a plastically deformable flat support (10); 
     said flat support (10) is applied, by being deformed, against said surface (20) of complex shape; and 
     said deformed flat support is connected to said surface (20) of complex shape. 
     The invention finds an advantageous application in the production of reflectors for antennas.

The present invention relates to processes for making an assembly ofconductive patterns on an insulating surface of complex form and, inparticular, for making printed circuits presenting a complex surfacewhich, a priori, is not developable, for example those which are usedfor making reflectors of antennas with discrete resonant elementsdistributed over surfaces of conical, parabolic, hyperbolic, etc . . .type, or those which enter in the structure of complex antennascomprising primary reflectors and secondary reflectors, as in theassemblies known to technicians under the names of Newton, Cassegrain,etc. assemblies.

Several processes to that end already exist. One of them consists inmaking conductive patterns on a supple, flat support, for example anelastomer. This supple support is then drawn then glued on a formidentical to that which is to be obtained. Another process consists inmaking the conductive patterns on a rigid support, for example a stripof a film of material known under the name KAPTON. This support is thencut out into strips or sectors of reduced width, thus more easilydeformable. These strips are then glued on a substrate having thedefinitive form chosen. Finally, the process is known which consists inmachining a metallized surface coated with a protecting varnish andsuperficially engraved mechanically along the contour of the desiredpatterns. Those parts which are not operative are then eliminated, likea skin, this operation generally being carried out manually.

It is obvious that these processes present drawbacks, for example, forthe first process, a poor resistance of the conductive patterns,particularly in the event of considerable variations in temperature. Theother two processes seem more reliable, but the complexity of theirembodiment does not render them industrializable and they can only beused punctually.

The present invention has for its object a process for making printedcircuits presenting a complex surface which is non-developable ordevelopable only with great difficulty, which overcomes the drawbacks ofthe known processes, whilst conserving certain of their qualities.

More precisely, the present invention has for its object a process formaking an assembly of electrically conductive patterns on anelectrically insulating surface of complex form, noteworthy in that:

said assembly of patterns is formed on a face of a plasticallydeformable flat support;

said flat support is applied, by being deformed, against said surface ofcomplex form; and

said deformed flat support is connected with said surface of complexform.

The Figures of the accompanying drawing will clearly show how theinvention may be carried out. In these Figures, identical referencesdesignate like elements.

FIG. 1 shows an antenna reflector in which the product obtained by theprocess according to the invention finds a particularly advantageousapplication.

FIGS. 2 to 7 show diagrams illustrating the different successive stepsof carrying out the process according to the invention.

FIGS. 8 to 12 represent different embodiments which may be obtained withthe process according to the invention.

The present invention concerns a process for making printed circuitspresenting complex surfaces which are non-developpable or at leastfairly difficult to develop. These circuits are of very great importancein modern techniques and are in particular currently used in reflectorsof antennas 1 such as the one illustrated in FIG. 1. This reflector 1 ismounted on a support 2, which cooperates with a support surface 3 viaarms 4. The reflector 1 presents a surface which is non-developpable inshape, for example paraboloid 5. The surface 6 of this paraboloid isconstituted by a support 7 made of an electrically insulating materialcomprising on its surface 8 patterns 9 which, themselves, areelectrically conductive. By way of example, patterns in the form ofcrosses have been shown, but it is obvious that these patterns may be inany other shapes necessary for the technicians.

In order to make such electrically conductive patterns, the process asdescribed hereinafter is advantageously used, which, with respect to theprocesses of the prior art, gives very good results, but which presentsthe additional advantage of being able to be industrialized forlarge-scale production.

The different principal phases of the process are shown in FIGS. 2 to 7.

The process consists, in a first stage, in making a first flat support10 whose dimensions are close to those which must be obtained for makingthe complex surface (FIG. 2). This first support must be deformable and,if it is made of a metallic material, must be able to be annealed. Itmay thus be constituted by a copper foil having a thickness of the orderof 10 to 40 microns.

In a second step (FIG. 3), there is then deposited on this first support10 a layer of a first given material 11, for example a varnish,defining, in this first material, zones 12 corresponding to the shape ofa giver circuit. In order to obtain these zones 12, it is possible todeposit the first material over the whole surface of the first supportand then to define the zones therein, for example by photo-engraving orsilk-screen process.

By way of example, the shape of the circuit illustrated is a cross, butit is obvious that it may be any other: circular, elliptic, square, etc. . .

When this second step is terminated, in a third step, a second material13 is deposited in these zones in order to cover the whole bottomthereof, over a thickness smaller than that of the first material 11(FIG. 4). By way of example, this second material may be gold, silver,nickel, aluminium or tin, which are good electrically conductivematerials and among those which are most advantageously used for theapplication mentioned hereinbefore, and the thickness may be of somemicrons. Moreover, if the second material 13 is one of the threementioned previously, it may advantageously be deposited by anelectro-chemical process presenting the advantage, at the same time, ofconnecting the layer of this second material with the surface of thefirst support 10.

Having arrived at this stage, the process then consists, in a fourthphase, in eliminating the layer of the first material 11, withouteliminating the second material 13 (FIG. 5). To that end, the twomaterials are chosen to be respectively attackable and non-attackable bya certain product. If the first material is a varnish and the secondgold, the layer 11 may easily be eliminated by the action of a solventnot attacking the gold. This technique is, moreover, well known per seand will therefore not be described in greater detail.

At this stage, a still flat support 10 is therefore obtained whichcomprises, in relief on a face 15, all the patterns 16 having the shapeof the zones which had been defined in the layer of the first material11 originally deposited on this face 15.

In a fifth stage, the edges 17 of the first support 10 comprising thepatterns 16 are gripped firmly in a frame 18 (FIG. 6) and the assemblyof these two elements, support 10 and patterns 16, is applied on asecond support 19, for example a substrate of composite materialreinforced with glass fibers or aramide fibers such as those known underthe trade name KEVLAR. This support 19 is such that its face 20 has theprofile of the complex shape of the surface of the printed circuithaving to be finally obtained. On the frame 18 are then applied effortsshown schematically by arrows 21, in order to deform the first support10 and to give it the shape of this complex surface 20, by applying itagainst the face 20 of the second support 19.

The assembly of the two elements, first support and patterns, is, ofcourse, connected by any means, for example glue previously spread overthe face 20 of the second support 19.

In the example illustrated, the complex shape is a convex surface but itmay be of any other shape.

When this fifth step is terminated, the material of the first support 10is eliminated, so as to conserve on the second support ofnon-electrically conductive material, only the predetermined patterns 16made of conductive material. If the first support is made of copper andthe patterns of gold, the copper is eliminated by chemical attack with asolution of iron perchloride or an alkali solution. This operation mayalso be used with a first support made of aluminium.

FIGS. 8, 9 and 10, 11 show two modes of application of the first support10 supporting the patterns 16 on the second support 19 made ofnon-conductive material.

FIGS. 8 and 9 show a first mode of application. The assembly comprisingthe first support 10 with the patterns 16 is applied on the face 20 ofthe second support, so that the patterns 16 are in contact with thisface, for example glued thereon (FIG. 8). In that case, the firstsupport is attacked by the chemical product and, finally, there remainonly patterns 16 on the face 20 of the second support (FIG. 9).

FIGS. 10 and 11 show another mode of application, in which the assemblyof the support 10 and the patterns 16 is disposed on the second support19 so that the first support 10 is itself directly glued on the face 20of this second support. The material of the first support is thenchemically attacked in the same manner as hereinabove. However, in thiscase, the patterns 16 remain located on columns 21 of material of thefirst support coming from parts of this first support which were notattacked chemically, since they were protected by the material of thepatterns 16 which is itself non-attackable by the chemical productchosen for eliminating the material of the first support.

It should be specified that the Figures have been elaborated only toillustrate the different steps of carrying out the process and to enableit to be more readily understood, but that in no way do they intend togive a perfect representation, to scale, of the different thicknesses ofthe different layers of materials.

In the embodiment given hereinabove, and up to the final result asillustrated in FIGS. 8 and 9, it is sometimes advantageous to choose thefirst support in a material of organic type, such as a thermoplasticsresin. In that case, the assembly of the first support 10 and patterns16 is advantageously disposed on the second support 19 in accordancewith the mode of application illustrated in FIG. 8. In fact, thematerial constituting the first support not being electricallyconductive, it is not necessary to eliminate it and if, in addition, thesecond support is chosen to be made of this same material (FIG. 12),adherence of the patterns may be obtained by simultaneous heating of thetwo supports until at least a partial fusion 22 is obtainedtherebetween, the patterns 16 then being imprisoned in thisnon-conductive material protecting them from any action of outsideagents, which enables them to be made of any conductive material, evenoxidizable.

The foregoing description shows all the advantages of the processaccording to the invention, in particular the fact that it makes itpossible to solve the problems raised in modern technology for obtainingindustrial production of printed circuits disposed on complex surfaceswhich are very difficult to develop, in particular for making reflectorsof antennas of which one has been chosen, in the description, by way ofexample of application.

I claim:
 1. Method for making an assembly of electrically conductivepatterns on an electrically insulating non-developable surface,comprising the steps of:(a) forming said assembly of patterns on a faceof a plastically deformable flat support; (b) applying said flatsupport, while being deformed, against said non-developable surface; and(c) connecting said deformed flat support to said non-developablesurface.
 2. Method as claimed in claim 1 wherein said deformable flatsupport is applied against said non-developable surface and connectedtherewith by its face bearing said patterns, and further comprising thestep of:(d) totally eliminating said deformed flat support.
 3. Method asclaimed in claim 1 wherein said deformable flat support is appliedagainst said non-developable surface and connected therewith by its faceopposite the one bearing said patterns, and further comprising the stepof:(d) eliminating said deformed flat support, except plumb with saidpatterns.
 4. Method as claimed in claim 1 wherein step (a)comprises:depositing on said flat support a first layer in which is madean assembly of recesses in register with said assembly of patterns;depositing in said recesses a second electrically conductive layer; andeliminating said first layer.
 5. Method as claimed in claim 4 whereinsaid recesses are defined by photo-engraving or serigraphy.
 6. Method asclaimed in claim 1 wherein step (c) is carried out by gluing.
 7. Methodas claimed in claim 1 wherein step (c) is carried out by fusion byheating.
 8. Method as claimed in claim 3 wherein step (d) is carried outby chemical attack.
 9. Method as claimed in claim 1 wherein saidplastically deformable flat support is a foil having a thickness ofbetween 10 and 40 microns.
 10. Method as claimed in claim 1 wherein saidplastically deformable flat support is a foil of annealed copper. 11.Method as claimed in claim 1 wherein said plastically deformable flatsupport is a foil of thermoplastics resin.
 12. Method as claimed inclaim 1 wherein said deformable flat support is made of an electricallyinsulating material and is applied against said non-developable surfaceand connected therewith by its face opposite the one bearing saidpatterns, said support being maintained on said surface as protection ofsaid patterns.
 13. Method as claimed in claim 1 wherein said patternsare made of a metal which is gold, silver, nickel, aluminum or tin. 14.Method as claimed in claim 1 wherein said patterns are made by chemicalor electro-chemical deposit.